This is a Shannon Award providing partial support for the research projects that fall short of the assigned institute's funding range but are in the margin of excellence. The Shannon Award is intended to provide support to test the feasibility of the approach; develop further tests and refine research techniques; perform secondary analysis of available data sets; or conduct discrete projects that can demonstrate the PI's research capabilities or lend additional weight to an already meritorious application. The abstract below is taken from the original document submitted by the principal investigator. The long term goal of this work is to understand rapid delivery of specific plasma membrane proteins, including growth factor receptors, to lysosomes. P-selectin, a cell adhesion protein involved in inflammation, is rapidly internalized, and then sorted constitutively in endosomes from recycling membrane proteins, delivered to lysosomes and degraded. The cytoplasmic domain of P-selectin contains a sorting determinant that is necessary and sufficient to drive rapid constitutive lysosomal targeting. The primary goal of this proposal is to develop a detailed understanding of the rapid constitutive targeting of P-selectin to lysosomes. The central hypothesis is that sorting of P-selectin in endosomes resembles mechanistically the selective localization of receptors to clathrin coated pits at the cell surface and the trans-Golgi network, which is mediated by specific interactions between the cytoplasmic domains of the receptors and "sorting machinery" proteins associated with the sorting organelle. The work will employ a combination of molecular, biochemical and cell biological approaches to explore the mechanism of rapid constitutive lysosomal targeting. The specific aims are to: 1. determine the exact site at which P-selectin is sorted from efficiently recycled membrane proteins; 2. identify proteins that interact specifically with P-selectin to mediate lysosomal targeting. P-selectins represents the first clear example of a plasma membrane protein that is efficiently targeted to lysosomes for degradation in the absence of activated signaling pathways. The evidence suggests that rapid constitutive degradation of specific plasma membrane proteins occurs in all mammalian cell types. This defines an as yet uncharacterized activity of endosomes, and may identify a novel class of short-lived plasma membrane proteins. Understanding the basis for rapid lysosomal targeting of plasma membrane proteins is important for many reasons. The first is to understand membrane protein sorting, an essential feature of cell organization and organelle function. The second is to understand regulation of selectin activity, which is one aspect of normal and pathological inflammatory responses. The third is that rapid constitutive targeting of selectins to lysosomes may provide a useful model for understanding the mechanism of receptor down regulation, a key process regulating many stages of development, cell differentiation and cell cycle regulation. Growth factor receptors use the same machinery, clathrin coated pits, for rapid internalization upon ligand binding that is used constitutively by P-selectin and other receptors. An important future goal of this work will be to determine whether the machinery that targets P-selectin to lysosomes constitutively also participates in down regulation of growth factor receptors.